Satellite Constellations 2 Workshop

Photo of a bright double star centered in a star field. Dozens of vertical tracks cut across the image.
This composite image shows the double star Albireo in Cygnus and was taken on 26 December 2019. Two out of ten 2.5-minute exposures recorded Starlink satellites moving across the field. Courtesy Rafael Schmall.


The Satellite Constellations 2 (SATCON2) workshop was held virtually 12–16 July 2021 to discuss how to implement the mitigation strategies that emerged from SATCON1 to minimize the negative impacts of satellite constellations on astronomy and the night sky.

Post-Workshop Press Conference

SATCON2, the successor workshop to last year's SATCON1, had three objectives:

  1. Define and quantify resources, metrics, and collaborations needed to implement the SATCON1 recommendations, many of which will require substantial effort and funds to address.
  2. Engage astronomers and satellite operators collaboratively in exploring policy frameworks and developing policy strategies for operations in low Earth orbit (LEO).
  3. Increase the diversity of stakeholders and perspectives contributing to address both the challenges and the opportunities that the industrialization of space creates for astronomers, satellite operators, and all of humanity.

From May through early July 2021, four working groups explored topics relevant to these goals:

  • The Observations Group (chaired by Meredith Rawls, University of Washington & Vera C. Rubin Observatory) worked to develop a plan for the implementation of Recommendations 8–10 in the SATCON1 report. The plan will define (1) optimal strategies for observations of LEO satellites, (2) the structure and resources required of an observing network of professional and amateur astronomers, and (3) the requirements for publicly accessible satellite positional information.
  • The Algorithms Group (co-chaired by Jonathan McDowell, Center for Astrophysics, and Robert Seaman, University of Arizona) worked to develop a plan for the implementation of Recommendations 1–3 in the SATCON1 report (though the group may examine any of the SATCON1 recommendations at its discretion). The plan will define the resources and timescale for developing the recommended applications.
  • The Community Engagement Group (co-chaired by Aparna Venkatesan, University of California, San Francisco, and James Lowenthal, Smith College) worked to engage a wide set of constituents in our shared goals for dark skies and a sustainable presence in space. This reaches beyond professional astronomy and commercial use to amateur astronomy, dark skies advocacy, K-12 education, fair access to space for minoritized communities, cultural practices, and sky traditions of indigenous tribes. This group will identify key issues impacting these constituencies and lay a foundation for ongoing communication and collaboration to preserve space as a scientific, environmental and cultural resource for humanity.
  • The Policy Group (chaired by Richard Green, Steward Observatory, University of Arizona) worked to review existing national policies and legislative frameworks. With the SATCON1 recommendations as context, the group will assess policy options to serve the diverse requirements of astronomy, the satellite industry, and other communities.

The working groups presented draft proposals for discussion at SATCON2, and the final results will be summarized in a written report some months after the workshop.

A virtual press conference was held upon completion of the workshop on 16 July 2021. See the links at the top of this page.

SATCON2 was funded by the National Science Foundation (NSF) and the American Astronomical Society (AAS) and is hosted by NSF's NOIRLab and the AAS. Jeffrey Hall (Lowell Observatory) and Constance Walker (NSF’s NOIRLab) are the workshop’s co-chairs.


Here is the full report.

1. For Observatories

Recommendation 1

Support development of an application available to the general astronomy community to identify and mask satellite trails in images on the basis of user-supplied parameters.

Recommendation 2

Support development of an application for observation planning available to the general astronomy community that predicts the time and projection of satellite transits through an image, given celestial position, time of night, exposure length, and field of view, based on the public database of ephemerides. Current simulation work provides a strong basis for the development of such an application.

Recommendation 3

Support selected detailed simulations of the effects on data analysis systematics and data reduction S/N impacts of masked trails on scientific programs affected by satellite constellations. Aggregation of results should identify any lower thresholds for the brightness or rate of occurrence of satellite trails that would significantly reduce their negative impact on the observations.

2. For Constellation Operators

Recommendation 4

LEOsat operators should perform adequate laboratory Bi-directional Reflectance Distribution Function (BRDF) measurements as part of their satellite design and development phase. This would be particularly effective when paired with a reflectance simulation analysis.

Recommendation 5

Reflected sunlight must be slowly varying with orbital phase as recorded by high etendue (effective area × field of view), large-aperture ground-based telescopes to be fainter than 7.0 V mag +2.5 × log(rorbit / 550 km), equivalent to 44 × (550 km / rorbit) watts/steradian.

Recommendation 6

Operators must make best effort for no specular reflection (flares) in the direction of observatories. If such flares do occur, accurate timing information from ground-based observing will be required for avoidance.

Recommendation 7

Pointing avoidance by observatories is achieved most readily if the immediate post-launch satellite configuration is clumped as tightly as possible consistent with safety, affording rapid passage of the train through a given pointing area.

3. For Observatories and Operators in Collaboration

Recommendation 8

Support an immediate coordinated effort for optical observations of LEOsat constellation members, to characterize both slowly and rapidly varying reflectivity and the effectiveness of experimental mitigations. Such observations require facilities spread over latitude and longitude to capture sun-angle-dependent effects. In the longer term, support a comprehensive satellite constellation observing network with uniform observing and data reduction protocols for feedback to operators and astronomical programs. Mature constellations will have the added complexity of deorbiting of the units and on-orbit aging, requiring ongoing monitoring.

Recommendation 9

Determine the cadence and quality of updated positional information or processed telemetry, distribution, and predictive modeling required to achieve substantial improvement (by a factor of about 10) in publicly available cross-track positional determination.

Recommendation 10

Adopt a new standard format for ephemerides beyond two-line-elements (TLEs) in order to include covariances and other useful information. The application noted in Recommendation 2 should be compatible with this format and include the appropriate errors.